Preparing suture materials



Patented Apr. 21, 1942 PREPARING SUTURE MATERIALS Peter D. Plambeck, Chicago, 111., assignor to Armour and Company, Chicago, 111., a corporation of Illinois No Drawing.

Application July 19, 1939,

Serial No. 285,458

6 Claims.

This invention relates to processes of preparing strand-like materials, such as sutures, ligatures, cords, tennis strings, violin strings, and the like from animal fibrous material, and it comprises processes wherein the fibrous material is spun into, a strand and the strand subjected to,chemicaltreatment under conditions which do not change the fiber angle in such strand; it further compris s processes wherein such animal fibrous mater al is twisted into strands or cords, and the cords subjected to mild alkaline treatment in a ,"plurality of treating solutions of progressively increasing strength, the treated cord thereafter being deplumped and dried.

In the art of making cord-like materials from animal fibers two general methods have been used. In one, pasty masses of hydrolyzed animal .fibers are extruded in the form of filaments or cords and dried. In the other, animal fibrous material is spun and twisted in much the same way as textile fibers are processed to' give cords, and these cords are then subjected to chemical treatment. The present invention is concerned with the latter type of process, and is more particularly concerned with the preparation of strong cords or strands from animal sinew material. While the process of the present invention will be more particularly described with reference to starting material composed of animal sinews or tendons, it will be understood that 7 other fibrous material of animal origin can be methods of carding, forming a roving, and twisting have not given products which are as satisfactory as ordinary cat gut. They lack tensile strength and knot strength. What the art has desired is some way of making vii-hat might be referred to as a cat-gut substitute from animal sinews, but giving a product better than cat gut. In the past, others have formed the sinew material into an assembled fiber strand and thereafter subjected the strand to chemical treatments causing the fiber mass to become homo geneous throughout. Such chemical treatment has been for the purpose of swelling the fibers and thereafter shrinking them back to normal size. However, the chemical treatments hitherto used have been so drastic that the finalprodnot loses much in fiber strength. The chemically treated cord is not as good as cat gut with regard to tensile strength and knot strength. The common chemicals used for the fibrous treatment have been alkaline in reaction since alkalis will swell the sinew material, and thereafter the swollen strand has been subjected to deplumping agents which cause the strands to shrink to normal size.

I have endeavored to find out why alkali treated sinew cords have lost tensile and knot strength and as a result of my discoveries I have been able to process the assembled fibers so that tensile and knot strength is greatly increased.

The present invention is based in part upon the discovery that the drastic alkaline treating processes of the past have markedly changed the fiber relationship, or so-called fiber angle in the twisted cords, and as a result of such changes the cord has lost its tensile and knot strength. I have discovered that the fiber angle changes because the swollen fibers are made quite slippery by the alkali and tend to slide on each other, thus causing movement of the individual fibers away from the original fiber'angle in the cord. Significant changes in the internal arrangement of the fibers in the strand resulting in change of strength characteristics therefore follow.

And, in accordance with the present invention, I avoid changes in the fiber angle of the preassembled cord by so conducting the alkaline treatment that it is far less drastic than has hitherto been used, and, in consequence, the initial fiber angle in the assembled cord is maintained throughout the treating steps.

In order that my invention may be more clearly understood at this point I shall briefly discuss what is meant by fiber angle.

In the preparation of textile threads and also cords, filaments, sutures, and the like from animal sinew material the fibrous starting material is first shredded. In the case of tendons the capsule or tendon sheath thereof is first opened up by a mechanical hammering action and the interior fiber shredded. These shredded fibers are'than carded in a carding machine and formed into a roving. The rovings are passed to a spinning machine from which they issue as a fine yarn. Several strands of the yarn are then twisted into the final cord. See for example, U. S. Patent 1,994,641. It is this cord which is then subjected to alkaline treatment. It is well known in the art that for best results with respect to tensile strength certain precautions should be exercised in forming the cord from the several strands of yarn in the twisting machine. By'trial and error those skilled in the art find that fiber angle which gives the best results with respect to tensile strength and knot strength. Fiber angle can be looked upon as the angular relationship between the direction of the fibers in the cord and the cross section of the cord, or as the angle made by the fibers and the axis of the cord. 'The cord should not be twisted so that the fibers lie at an angle of nearly 90 with respect to the axis of the cord, nor should they lie parallel to the axis of the cord. While the fiber angle is not readily measured those skilled in the art have determined the most satisfactory twist for a given result. If the string has a higher twist than the optimum the tensile strength may be increased with some loss, however, in the knot strength. If the fibers are aligned more nearly parallel to the axis of the cord the knot strength will be increased with some loss in the tensile strength. In consequence, it has been common practice in the art to put the right amount of twist in the cords which gives fiber angles best effecting a compromise between knot strength and tensile strength.

As stated, it has been common to subject such assembled cords to alkaline treatment, and such assembled cords have lost optimum tensile strength and knot strength because of changes in the fiber angle set up by the alkaline treatment. The present process is, accordingly, based upon the discovery that very mild alkaline treatments will maintain the fiber angle and thus avoid loss in tensile or knot strength. Chemical treatment, as stated, is necessary before a satisfactory spun and twisted sinew cord can be prepared. It is the chemical treatment which converts the twisted cord to a homogeneous solid string similar to catgut in appearance and other characteristics, and which can be used as a suture, tennis string, strings for musical instruments, and the like. In the present invention I make use of certain facts which I have discovered. One is that the maximum pH value of the alkaline solutions used for rendering the cord homogeneous should not exceed l3. Accurate temperature control during the alkaline treatment is also essential. The cord should be passed through separate alkaline solutions of progressively increasing strength under controlled temperature conditions, and the cord should preferably be subjected to wetting with pure water prior to the alkaline treatment.

In this specification I refer to cords and fiber strands interchangeably. What I mean is a cord or strand which has been prepared by carding, roving, twisting the roving to a yarn and then preparing the cord or strand from a plurality of yarn strands. In every case the material treated by the present process is composed of a twisted strand or cord.

As an example of carrying out my process I take the fiber strand which has been assembled in the usual way by shredding, carding, twisting and spinning sinew fibers (as described in U. S. 1,999,641) and place it in substantially neutral water at 70 F. and allow to stand for 45 minutes in order to wet the fibers thoroughly, thus preparing them for proper penetration by the treating agents to follow. The strand is removed from the water bath and immediately placed in a 0.01% NaOH solution (pH 10.0 to 10.5) at 86 F. and allow to stand for 30 minutes. The strand is then transferred to a 0.02% NaOI-I solution strength. If the chemical treatment is such that (pH 11.0 to 11.5) which is also at 86 F. and allowed to stand for 30 minutes, after which it is transferred to a 0.03% NaOH solution (pH 11.5 to 12.0) at F. and allowed to stand for 30 minutes. At this point the strand will be preceptibly swollen and will be somewhat translucent. It is now placed in a 0.04% NaOH solution (pH 11.75 to 13.0) at 97 F. and allowed to stand for 30 minutes. The strand will be seen to be quite translucent and definitely sfilen. In order to deplump and neutralize the ltrand is now placed in a 0.4% solution of NaHCO: (pH 7.5 to 8.5) at 86" F. and held for another 30 minutes. At the end of this time the strand will be observed to have shrunk to its normal size and to have become completely opaque. In order to insure complete neutralization, the strand is then given a final treatment by immersing it for 30 minutes in a fresh 0.4% NaHCOa solution (pH 7.5 to 8.5) at 83 F. It is then allowed to stand in a large amount of approximately neutral water for from 12-18 hours at 36 F. in order to wash out final traces of salt, at the same time inhibiting swelling (due to the action of the medium at room temperatures) and bacterial action.

The strand will then be ready for drying, a .'.'!..e...-..v

polishing and other further finishing known to the art.

It will be understood that the temperatures recited above can vary within certainlimits. That is, the first water treatment can take place at from 50 F. to 70 F. but preferably not above 70 F. in order that no swelling will take place at this stage. The treatment with 0.01% alkali may take place at from 83 to 87 F.; that with 0.02% alkali, at from 83 to 87 F.; that with 0.03% alkali, at from 88 to 92 F.; that with 0.04% alkali, at from 95 to 99 F. and a temperature as high as 100 F. must be avoided as this temperature has been found to be critical for collagen. The temperature of the first neutralizing bath should be from 85 to 89 F. and, of the second, from 83 to 85 F.

The time will be limited by the appearance of the string at the given stage. Other alkalies can be substituted for the sodium hydroxide other alkaline bicarbonates may be used the pH values stated are maintained.

It is an advantage that the tempera the neutralizing or deplumping bathibe less' I that of the final alkaline swelling bath'becaiise in this way I get a thermotic deplumping effect also.

Thus, from the foregoing example, it will be apparent that the broad aspects of the above invention consist in producing homogeneous cord-like material from preassembled collagenous fibrous strands by a series of treatments with baths of increasing alkaline concentration within critical ranges of temperatures, followed by deplumping. Although the temperatures and concentrations are quite critical, nevertheless, it is to be expected that others may employ the principles of the present invention without using the exact temperatures and concentrations given above. As stated, the essential requirement of the invention is that fiber angles be maintained without change throughout the treatment process. ing strand is homogeneous and has satisfactory the fiber angle is changed then the underlying obiects of the present invention are defeated.

If, instead of using a plurality of alkaline solutions of increasing strength, I process the When this condition is fulfilled the resultstrand in a single bath, results are not satisfactory. If a single bath of 0.04% NaOH is used the strand may look satisfactory by visual inspection, but it is not homogeneous and deplacement in the fiber angle has occurred. Consequently, for obtaining the results of this invention care must be taken to avoid any fiber angle displacement.

Having thus described my invention, what I claim is:

1. In the treatment of twisted strands of col- 'lagenous animal fibrous material with alkaline swelling agents to render the strand homogeneous, and thereafter treating the swollen strand with deplumping agents to shrink the strand so that the original angular relationship of the fibers is maintained, the process which comprises immersing the strands in an alkaline solution having a pH of about to 10.5, then immersing the strands in a solution having a -pH of about 11 to 11.5, then immersing the strands in a solution having a pH of about 11.5 to 12, and finally immersing the strands in a solution having a pH of about 11.75 to 13.0 and then subjecting the swollen strands to deplumping the temperature during the aforesaid treatment not exceeding the breakdown temperature for collagen.

2. In the treatment of twisted strands of collagenous animal fibrous material with alkaline swelling agents to render the strand homogeneous, and thereafter treating the swollen strand with deplumping agents to shrink the strand, the process which comprises immersing the strand in substantially neutral water at a temperature of about F. to F., then immersing the strands in a caustic alkali solution having a pH of about 10 to 10.5 at a temperature of about 83 F. to 87 F., then immersing the strand in a caustic alkali solution having a pH of about 11 to 11.5 and a temperature of 83 to 87 F., then immersing the strand in a caustic alkali solution having a pH of about 11.5 to 12 and a temperature of 88 F. to 92 F., then immersing the strand in a caustic alkali solution having a pH of about 11.75 to 13.0 and a temperature of about 95 F. to 99 F., but below 100 F., and then shrinking the strands by immersing them in a solution having a pH of about 7.5 to 8.5

3. The process of treating twisted strands of collagenous animal fibrous material to render the same homogeneous while avoiding any substantial change in the original angular relationship of the fibers, which comprises subjecting the strand to the action of a plurality of alkaline solutions of increasing strength ranging from a pH of about 10 to a pH of about 13, the temperature of the last bath being higher than that of the first but not exceeding the breakdown tempera,- ture for collagen, deplumping the strands, holding the strands in cold Water to inhibit swelling, and drying the strands.

4. The process of treating twisted strands of collagenous animal fibrous material to render the same homogeneous while avoiding any substantial change in the original angular relationship of the fibers, which comprises subjecting the strand to the action of a plurality of alkaline solutions of increasing strength ranging from a pH of about 10 to a pH of about 13 and the temperatures of the solutions increasing from about 83 F. to about 99 F., and then deplumping the thus treated strands, holding the strands in cold water to inhibit swelling, and drying the strands.

5. The process as in claim 3 wherein the strand is first immersed in water and then in the alkaline solutions.

6. The process as in claim 4 wherein the strand is first immersed in water and'then in the alkaline solutions.

1 PETER D. PLAMBECK. 

